1. Making friends with IDL IDL is an interpreted rather than a compiled language. This means that large IDL programs can execute less rapidly than equivalent compiled programs written in FORTRAN or C. IDL LIMITATIONS: IDL is a proprietary system (need licence) interactive environment excellent for visualizing, analyzing, editing, and displaying numerical data sets immediate access to all variables optimized array operations versatile built-in plotting and graphics routines data structures possible interface with C and Fortran routines on line help (?) IDL = interactive data language

2. Making friends with IDL create variables > name = ‘Maxwell’ creates a string > z = 1.0e-8 creates a scalar > testdata = fltarr(512,512) creates a 512x512 2-D array with zero entries > a = [1,2,3] creates a vector > a = [a,4] expands a vector Warning: If you redefine a variables during your work, you lose the previous values Avoid operation with different variables types. For example using float and integer these could be different > print, 3.456 * 1 > print, 3.456 * 1.

3. Variables Variable names can have letters, numbers and underscores in them. They are NOT case-sensitive: aaa, Aaa and AAA are all the same variable. IDL> a=[3, 5, 6, 2.5, 100, 27.7] IDL> a= [[ 2,3,4],[10,20,30]] IDL> a=float(b) IDL> a=fltarr(n_elements(b),4,2)‏ Array index START FROM 0!!!! Array of 2 rows and 3 columns = Array[3,2] One dimension array of 6 elements = Array[6]

4. Array manipulations INVERT - Computes the inverse of a square array. MAX - Returns the value of the largest element of Array. MEDIAN - Returns the median value of Array or applies a median filter. MEAN – Return the mean value (also first element of MOMENT). MIN - Returns the value of the smallest element of an array. MOMENT – compute the first 4 moments (mean, variance…) REFORM - Changes array dimensions without changing the total number of elements. REVERSE- Reverses the order of one dimension of an array. SIZE- Returns array size and type information. TOTAL - Sums of the elements of an array. TRANSPOSE - Transposes an array. WHERE- Returns subscripts of nonzero array elements. (a b c)## (g h) = (ag+bi+ck ah+bj+cl) (d e f) (i j) (dg+ei+fk dh+ej+fl) (k l) (a b c)# (g h) = (ag+dh bg+ch cg+fh) (d e f) (i j) (ai+dj bi+ej ci+fj) (k l) (cg+fh ci+fj ck+fl) > a = [1,2,3] > b = [4,5] > print, a#b > print, b#a > print, a##b > print,a*b > print,a+1 > print,b*2 > print,a+b Warning!!! Try to avoid loops t=0 for i=0,n_elements(a)-1 do t=t+a(i) t=total(a)

5. looking for help ? name help print help,variable : print variable informations. help,A,/str : print structure info help,/rou : prints list for all compiled procedures. Lists procedure and functions separately. help,/sy : prints current values of all "system variables", which are special variables known to all routines. Names of these begin with a "!", e.g. !dir, !path, etc. help,/rec : prints contents of command recall buffer in reverse order help,/dev : prints parameter settings for current graphics device help,/mem : lists current memory usage print,max(a); print,min(a); print,max(a); print,mean(a); print,variance(a); print,median(a); print,moment(a): print various statistical properties of image array. (moment prints first four moments.) Open a help on line windows and search for ‘name’

6. Saving data (and time!) save restore Safety idea: save your data!!! Be prepared: 99% of time you will have to redo plots. Usual sequence: 1) Make plot 2) Save data (and exit from idl) 3) Meeting 4) Restore data 5) Redo plot It will help also have your code saved in a routines. > save,variable1,variable2,variable3,filename=‘~elisa/idl/data.sav’ Keyword: ALL => save all common block, system variable and local variable from the current IDL session. > save,/all,filename=‘datatemp.sav’’  restore, filename=‘~elisa/idl/data.sav’ > restore,filename=‘datatmp.sav’ make a routine!

7. main routine procedures or subroutines functions As you type, each line is interpreted and immediately executed for (loop), if, case... parameters and keywords IDL routines (.pro) One of the best ways to learn how to write and use IDL programs is to look the existing IDL programs... end pro NAME, VARIABLES... end function NAME,VARIABLES... return,VALUE end >.r filename > name, variables > a = name (variables) NAME,input1,input2...output1,output2...keyword1=value1,$ keyword2=value2, /Keyword3.... optional and can be in any order.pro file requirement How to call it without.pro OR

8. Program execution (and other) all IDL procedures/functions are assumed to be in files with the explicit extension '.pro'. compiles the IDL procedure(s) or function(s) in the file [name].pro. If this is a main program, also executes it. IDL will locate the first file with this name in the IDL path or current directoryWARNING!!!! stop>.c or.con @file_name ; comment Values of keywords are usually determined by assignment statements: PROCEDURE_NAME,parm1,parm2.....KEYWORD1=100.,KEYWORD2='dumbo',... in the case of switches, keywords can be set to a value of 1 by using the following syntax: NAME,parm1,parm2...../KEYWORD1,..... > retall Run from IDL prompt Inside a file.pro Compile the file_name.pro Useful if the file mane is different from the procedure name >.r or.run [name] Don’t forget the comments!!! Comments begin with ‘;’ for debugging!!... print... plot... to continue if you wont to come back to the first level

9. Structures A structure can be thought of as a user-defined data type or groups of different data IDL allows you to put lots of variables into a single ‘structure’ dsat={aod550:aot,$; mean AOD stdaod550:sigma,$; standard deviation n:num,$; number of points latc:latitude,$; central lat of the boxes lonc:longitude}; central longitude of the boxes For example satellite data can be load as a structure containing: Instrument name, data and time, pixels radiances, coordinates and observing angles of the pixels Define a structure: A structure (e.g. dsat) is an ensamble of other, previously defined, variables (and structures) > help, dsat,/str AOD550 DOUBLE Array[720, 360] STDAOD550 DOUBLE Array[720, 360] N LONG Array[720, 360] LATC DOUBLE Array[360] LONC DOUBLE Array[720] > print,dsat.aod550(good) To access the variables of a structure Use: mone_str.nome_var Routine that read satellite data usually load a structure for any image/orbit keep related variables together pass/return a lot of variables with only one name

10. Basic plots window,0,xsize=300,ysize=200 x=findgen(10)‏ IDL> print,x 0.000 1.000 2.000 3.000 4.000 5.000 6.000 7.000 8.000 9.000 IDL> plot,sin(x2) x2=2*!PI/100*findgen(100)‏ seed=1l n=32 x=randomu(seed,n)‏ y=randomu(seed,n)‏ y2=randomu(seed,n)‏ plot,x,y,psym=1,title='Random XY Points' oplot,x,y2,psym=2,colour=2

11. Others useful things cut of data where good = where (time eq 1000.,count) if (count eq 1 ) then begin... If (count gt 1) then begin plot, x(good), y(good) endif and ; and... or ; or gt ; greater than (similarly lt) ge ; gt or equal to (similarly le) eq ; equal to ne ; not equal to Logical operator a = tvrd(true=3) write_jpeg, 'namefile.jpg',a,true=3 save a window like.jpg print on postscript.ps file set_plot, 'ps' device, filename='filename.ps‘ … close, /device set_plot, 'x' Smaller file, good to make presentations and movies, NOT good for reports and papers !!! ‘comp_map_'+sat1+'_vsall.jpg’ plotting commands png?

12. routines at AOPP mappoints,data,lat,lon,centre=[0,0],/nogrey,nlevels=100 loadxy loadxyz colour_ps /home/crun/eodg/idl/ tvdata ncol=4 nrow=4 !P.MULTI= [0,ncol,nrow,0,0] mappoints,dayav.AOD550,lat,lon,centre=[0,0],/nogrey,$ Nlevels=100,range=range,symsize=0.6,$ title='AOD all daset average '+strcompress(i+1)+' March 2006' avgrid,lat,lon,aod imagepoints,data,lat,lon fitexy,px,py,A,B,X_SIG=X_SIG,Y_SIG=Y_SIG Linear fit when both x and y have errors (y = A + B x) Plots data points, with defined latitudes and longitudes Interpolate data (with the associated lat,lon) onto a regular lat lon grid, and plot the image Using the same some fast regridding code (RAL) Load txt file in columns Set colour bar + several routine to load different type of data ASK!!!